Assign public IP to server on LAN that is behind router with periodically changing IP

Question

I plan to create following network configuration:

1. VPS-SSD Server at OVH (KVM based AFAIK):

   • Arch Linux
   • public IPV4 address P1 on eth0
   • public IPV4 adderss P2 (not assigned to any device)

2. Linksys EA3500 router with OpenWRT installed. Public dynamic IPv4 address D1 on WAN interface from DHCP, changed periodically by network provider.

   • One VLAN V1 for LAN users, using NAT (Wifi)
   • One VLAN V2 on single ethernet port for MailServer (separate Linux machine)

What I want to achieve is to Assign public P2 IPv4 address to MailServer.

I am not very good at networking but from three days research I see two possible solutions:

A. Create OpenVPN point-to-point link from D1 to P1 using tap interfaces. Bridge tap interfaces on VPSServer with eth0 and on EA3500 with VLAN V2 device. This way it should be possible to assign P2 address to MailServer.

B. Create GRE tunnel from EA3500 to VPSServer using P1 address as endpoint. At VPSServer configure routing to pass traffic to P2 using this tunnel. Assign P2 IPv4 address to MailServer.

Do you think any if it is doable? I am not sure if GRE tunnel can be set up if one of endpoint has a dynamic IP address. I think that OpenVPN solution is worse because it adds VPN encryption which I do not need at all.

If you have any better ideas how to set it up please share.

Answer 1

Ok, read what you wanted to do wrong the first time lol. Alright you still have an easy solution. Not sure where your separate Linux machine is at, and not sure why you don't have a public IP for it, if it is at OVH. They generally assign at least 1 public IP address to your dedicated servers. If you are running virtual machines, what you would do is just make a virtual nic on the host system, and then in the virtual machine being the mail server you would just bridge the connection to the virtual nic, which is already bridged to your phyiscal nic. But if you do indeed have 2 separate Dedicated servers, then they should both have at least 1 public IP address.